Steve Best
Well-Known Member
We are all used to pulling an engine apart and seeing thick buildups of carbon on the piston and head.
Something like this:
Even this is not as bad as we are used to. Note that is looks wet?
This was semi synthetic oil and the deposit was actually a thick tarry goo that wiped off the polished parts.
(note also a slight head gasket leak)
Here is what it looked like after wiping off:
I might have been able to clean the cast section better if I had used more elbow grease.
We are all used to the thick hard carbon build up from conventional oil, that can only be scraped off.
I put this head back on exactly as photographed and continued testing spark plugs on long trips.
Instead of semi-synthetic, I switched to Motul 800 full synthetic.
At about 70 kms (with about 500ml of semi synthetic mix fuel left in the tank) looks like this on the left:
On the right is an aftermarket head with much of a tank of fuel (about 80 kms) on it.
These deposits wiped off to clean metal with a paper towel.
Notice signs of the factory head leaking at the head gasket again. It runs at faster speeds 60-66 kph (9500rpm) whereas the head on the right runs 55-58 kph (8000rpm) with no detonation.
The head on the right has huge torque at very low speeds and keeps speeds on the hills better.
The head on the left's tendency to detonate at speed is probably what is stressing the headgasket, as well as being weak in the fore/aft plane. The head on the right has no tendency to detonate and keeps rpm under 9000rpm, very good things for longevity.
This is not the first time I have seen this. Here are pictures from my KTM 125:
Left is 7 years of Ipone and Motul full synthetic and rich fuel jetting.
Center is from a used motocross KTM 125 bike I bought, conventional oil, rich jetting.
Right is several years and thousands of street and trail kms (note the headgasket) with Ipone and Motul full synthetic and lean jetting.
Steve
Something like this:
Even this is not as bad as we are used to. Note that is looks wet?
This was semi synthetic oil and the deposit was actually a thick tarry goo that wiped off the polished parts.
(note also a slight head gasket leak)
Here is what it looked like after wiping off:
I might have been able to clean the cast section better if I had used more elbow grease.
We are all used to the thick hard carbon build up from conventional oil, that can only be scraped off.
I put this head back on exactly as photographed and continued testing spark plugs on long trips.
Instead of semi-synthetic, I switched to Motul 800 full synthetic.
At about 70 kms (with about 500ml of semi synthetic mix fuel left in the tank) looks like this on the left:
On the right is an aftermarket head with much of a tank of fuel (about 80 kms) on it.
These deposits wiped off to clean metal with a paper towel.
Notice signs of the factory head leaking at the head gasket again. It runs at faster speeds 60-66 kph (9500rpm) whereas the head on the right runs 55-58 kph (8000rpm) with no detonation.
The head on the right has huge torque at very low speeds and keeps speeds on the hills better.
The head on the left's tendency to detonate at speed is probably what is stressing the headgasket, as well as being weak in the fore/aft plane. The head on the right has no tendency to detonate and keeps rpm under 9000rpm, very good things for longevity.
This is not the first time I have seen this. Here are pictures from my KTM 125:
Left is 7 years of Ipone and Motul full synthetic and rich fuel jetting.
Center is from a used motocross KTM 125 bike I bought, conventional oil, rich jetting.
Right is several years and thousands of street and trail kms (note the headgasket) with Ipone and Motul full synthetic and lean jetting.
Steve
Last edited: